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Investigation on the formation of microplastics from compostable plastic bags during the rotting process in field tests

Journal of Material Cycles and Waste Management 2025
Erwin Binner, Christian Zafiu, Peter Beigl, Benedikt Vay, Marion Huber-Humer

Summary

Researchers investigated whether compostable pre-collection plastic bags form microplastics during rotting under real-world field conditions, which often differ substantially from the controlled laboratory settings used in certification procedures like EN 13432. The study found that field composting conditions produced microplastic fragments, raising questions about the environmental claims of certified compostable plastics.

Abstract Compostable pre-collection plastic bags can foster the separate collection of biowaste from households and reduce pollution of conventional plastics. Test conditions proposed in certification procedures (e.g., EN 13432) used to show the compostability of such materials (and products) are made under controlled and optimal laboratory conditions and extended test periods that are rarely achieved in the composting practice. Thus, it is possible that some ‘compostable’ plastic products may not be degraded satisfactorily in technical composting plants under realistic conditions, which could leave microplastic fragments in composts. Therefore, in this study, the compostability of a certified compostable plastic bag was investigated under practical conditions in two state-of-art composting plants in Austria. Expected future plastic bag quantities (resulting in 0.95–1.19 kg biowaste per pre-collection-bag) were added to test windrows and were investigated during 12 weeks for fragment sizes > 0.2 mm. The results show that the investigated materials degraded within the first four weeks and left only tiny amounts of plastic materials in a size range 0.63–0.2 mm.

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